Definition
A regulatory requirement that an aircraft operating in instrument flight conditions where icing is forecast or encountered must be equipped with functioning anti-ice or de-ice systems sufficient to keep critical surfaces, instruments, and engine intakes free of ice accumulation that would degrade flight or instrument performance. Critical items typically include the pitot tube, static ports, propeller, windshield, carburetor or induction system, wings, tail surfaces, and fuel vents.
Plain English
The aircraft must have working equipment to prevent or remove ice from the parts that matter — the wings, tail, propeller, engine air inlet, and the small openings that feed the flight instruments — before flying into clouds or weather where ice is expected.
Context Anchor
Seen in IFR equipment and operating requirements, especially when a flight may encounter freezing clouds, freezing rain, or other icing conditions.
Derivation
‘Adequate’ comes from the Latin adaequatus, meaning ‘made equal to’ — sufficient for the task at hand. In this context it means the protection must be equal to the icing conditions expected, not simply present. A pitot heat switch that doesn’t work, or a de-ice boot with a leak, is not ‘adequate’ even though the system exists on the aircraft.
Why Pilots Care
Without it, ice can block pitot tubes or static ports and produce incorrect airspeed or altitude information, removing the pilot's ability to maintain control when outside visual references are lost.
Grounding Statement
If ice can form on the airplane, the systems needed to fly safely by instruments must be protected well enough to keep doing their job.
Intuition Check
Do not read “adequate” as “best possible” or “guaranteed safe in any ice.” Here it means sufficient and appropriate for the aircraft, the equipment, and the expected icing conditions.
Example Sentence 1
Before filing IFR into the forecast freezing rain, the pilot confirmed that pitot heat, the propeller anti-ice, and the windshield defroster were all operational — adequate ice protection of IFR systems was a no-go item.
Example Sentence 2
Regulations require adequate ice protection of IFR systems on any aircraft used for instrument flight in known or forecast icing.